This invention relates to a process for the improved combustion of oil fuels which may include hydrocarbon oils, vegetable or plant oils, oil-coal slurries, and the like. Improved combustion is accomplished by incorporating a minor proportion of a separately prepared water-rich water-in-oil emulsion into a fuel prior to combustion, thus providing an optimized proportion of water present in the fuel as tiny droplets having a diameter within the range from about 1 to about 10 microns.
The benefits from the inclusion of water in fuels employed in furnaces, internal combustion engines, and gas turbines have been observed over many years and reported by many investigators. For example, Proceedings of the 16th International Symposium on Combustion, 1976, Combustion Institute, discusses water addition to fuels in papers appearing at pages 279-295, 297-305, 307-319, and 321-336, and presented by F. L. Dryer, A. Sjogren, M. T. Jacques et al., and G. Greeves et al., respectively.
The Dryer paper pointed out that the addition of water may have both physical and chemical kinetic effects. In spark ignition engines pre-ignition and detonation can be reduced. For furnace fuels, water shortens combustion time and improves the completeness of combustion. Applications to diesel engines, gas turbines and industrial boilers are discussed, employing up to 25 volume % water and 3% of surfactant (emulsifier). The Jacques, et al., paper reported on the addition of up to 15 volume % water together with asphaltenes. Carbonaceous residues were greatly reduced, presumably due to a lesser degree of thermal cracking during combustion of the subject fuels. The Greeves, et al., paper reported on diesel engine performance, noting a reduction in NO.sub.x production during combustion when water injection with the fuel was employed. Water/fuel volume ratios varied from 0.21 to 0.80, or 17.3 to 44.4 volume % water.
In general, the reported positive effects from addition of water to fuels include reduced fuel consumption, cleaner exhausts, cleaner boiler tubes, less luminosity and shorter flame length. Further substantiation is found in a recent report (March, 1985) from The Adelphi Research Center, Inc. where the addition of 10 volume % water to #6 residual fuel was studied in boiler furnaces.
Generally, these reports have found that large amounts of water, ranging from 10 to 40 volume %, are required to obtain significant reductions in carbon emissions and in improved combustion performance. One exception is the cited report by A. Sjogren who demonstrated that less water is required for significant combustion improvement where the water is more finely dispersed in the oil, preferably as particles having diameters in the range from 2 to 5 microns. This permitted the use of only 2-3 volume % water while substantially eliminating oil coke in the boiler emissions. Dispersion of water droplets in the oil fuel was effected by repeated and intense mechanical treatments, including ultrasonic homogenizing, mechanical homogenizing, or centrifugal pumping. Inclusion of a surfactant was also employed.
The ultrasonic formation of water-in-oil dispersions, with no added emulsifying agent, for use in burners is further described in U.S. Pat. No. 3,749,318. Similar usage of Venturi systems is disclosed in U.S. Pat. Nos. 3,937,445 and 4,416,610.
The prior art processes requiring the inclusion of some 10 to 40 volume % water in the oil fuel have not been widely employed because of significant problems. Additional heat is required to vaporize the large amounts of water, thus reducing furnace efficiency. Additional costs are incurred in the delivery and storage of emulsified fuels. Other problems include corrosion of storage facilities, stratification of the emulsion, and water separation. Corrosion, wear and damage to fuel system components is more serious where water is added to fuels employed in internal combustion engines.
The benefits attributed to combustion where only 2-3 volume % water is added to the fuel were obtained only when either multiple pass emulsification or intensive emulsification in the presence of an added agent was employed. Energy consumed in such emulsification and additional costs for specialized equipment and/or large proportions of emulsifying agents detract from the attractiveness of this approach to providing tiny droplets of water in the large volume of oil fuel to the combustion zone.